Seafloor-surface connecting installation of a submarine pipeline installed at great depth

ABSTRACT

The invention concerns a seafloor-surface connecting installation for a submarine pipeline ( 10 ) set on the seafloor, in particular at great depth, of the hybrid-tower type comprising a static base ( 13 - 18 ) set on the seabed. In the inventive installation: 1) said vertical riser includes a terminal pipe portion ( 5   1 ), and a flexible joint ( 19 ) which allows angular movements (α) of the upper part ( 5   2 ) relative to said terminal pipe portion ( 5   1 ); and 2) the terminal part ( 11 ) of said pipe resting on the seabed has a an elbow-type terminal curvature; 3) said terminal portion ( 5   1 ) of the vertical riser is connected to said terminal curvature ( 11 ) by a single connecting element; and 4) said base plate ( 13 - 18 ) rigidly maintains in fixed vertical position and linked to each other via said connecting element ( 12 ): said terminal pipe portion ( 5   1 ) and said elbow-type terminal curvature ( 12 ) the latter facing upwards.

PRIORITY CLAIM

This is a U.S. national stage of application No. PCT/FR02/00608, filedon Feb. 18. 2002. Priority is claimed on that application and on thefollowing application: Country: France, Application No.: 01/02206,Filed: 19 Feb. 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The object of the present invention is a seafloor—surface connectioninstallation of at least one sub-marine hybrid tower pipeline installedat great depth.

The technical field of the invention is the field of manufacturing andinstallation of production vertical risers for sub-marine extraction ofpetroleum, gas or other soluble or fusible material or of a suspensionof mineral material using an immersed well head for the development ofproduction fields installed on the open sea, offshore. The main andimmediate application of the invention being in the field of petroleumproduction.

A floating base comprises in general anchoring means for remaining inposition regardless of the currents, winds and the swell. In general, itcomprises also petroleum storage and processing means as well asoffloading means to the oil -tank carriers, these latter appearing atregular intervals in order to carry out removal of production. InEnglish these floating bases are called “Floating Production StorageOffloading”, for which the abbreviated form FPSO will be used throughoutthe following description.

By reason of the multiplicity of the lines existing on this type ofinstallation, seafloor—surface hybrid type vertical riser typeconnections have been deployed in which the substantially vertical rigidpipelines called herein ‘vertical risers’, assure the connection betweenthe sub-marine pipelines resting on the seafloor and rise along a riserup to a depth in proximity to the surface, at which depth the flexiblepipelines assure the connection between the top of the tower and thefloating base. The tower is thus equipped flotation mans in order toremain in a vertical position and the risers are connected at the footof the tower to the sub-marine pipelines by flexible sleeves that absorbthe angular movements of the tower. The assembly is collectively calleda ‘hybrid tower’, because it combines two technologies: on the one handa vertical part, the tower, in which the riser is comprised of rigidpipelines and on the other hand the top part of the riser comprised ofconcatenated flexible pipes that assure the connection to the floatingbase.

2. Discussion of Related Art

French patent FR 2 507 672 published on 17 Dec. 1982 entitled “Riser forGreat Water Depths” is well-known and describes such a hybrid column.

The present invention relates more particularly to the known field ofconnection of the type comprising a hybrid vertical column anchored onthe seafloor and comprised of a float disposed at the top of a verticalriser, the latter being connected by a pipeline, especially a flexiblepipeline assuming by its own weight the form of a catenary from the topof the riser up to a floating base installed on the surface.

The interest in such a hybrid column resides in the possibility for thefloating base to be able to leave its normal position by inducing aminimum of stress in the column as well as in the parts of the pipelinesin the form of suspended catenaries, both on the seafloor and on thesurface.

The patent filed on behalf of this applicant, WO 00/49267, is well knownand discloses a column whose float is at a depth greater than thehalf-depth of the water and whose catenary connection to the surfacecraft is realized by means of thick-walled rigid pipelines. The columnthus described requires at its base flexible link pipes enablingconnecting the lower end of the vertical risers of said column to thesub-marine pipeline resting on the bottom in such a fashion as to absorbthe movements resulting from dilations due to the temperature of thefluid being transported.

More particularly, in WO 00/049267, the anchoring system comprises avertical tendon comprised of either a cable or a metal bar or even of apipeline held at its upper end by a float. The lower end of the tendonis fixed to a foot resting on the seafloor. Said tendon comprises guidemeans disposed over its entire length through which said vertical riserspass. Said foot can be positioned simply on the seafloor and remain inplace in virtue of its own weight or it can be anchored by means ofpiles or any other suitable device for maintaining it in place. In WO00/42967 the lower end of the vertical riser can be connected to the endof a curved connection sleeve moveable between a high and a low positionrelative to said foot from which this connection sleeve is suspended andassociated with a return means moving it into the high position in theabsence of the riser. This mobility of the bent connection sleeve makesit possible to accommodate variations in the length of the riser underthe effects of temperature and pressure. An abutment device is securedat the top of the vertical riser in suspension on the support guideinstalled on the top of the float.

Furthermore, the crude petroleum traveling over very longdistances—several kilometers—it should be provided with an extremeinsulation level in order on the one hand to minimize the increase inviscosity that would lead to a reduction of the hourly production of thewells and on the other hand to prevent blockage of the flow bydeposition of paraffins or the formation of hydrates once thetemperature decreases to around 30-40° C. These latter phenomena areeven the more critical, in particular in West Africa, as the temperatureof the sea bottom is of the order of 4° C. and the crude petroleum areof the paraffin type.

Numerous thermal insulation systems are known that make it possible toachieve the required performance level and to resist the pressure at thebottom of the sea which is of the order of 150 bar at 1,500 m depth. The“pipe-in-pipe” concepts can be cited inter alia that comprise a pipecarrying hot fluid installed within a protective external pipe, thespace between the two pipes being either simply filled with a heatinsulating material, whether or not confined under vacuum, or simpleevacuated. Numerous other materials have been developed for assuringhigh performance insulation; certain of these being resistant topressure, simply surrounding the hot pipeline and are in generalconfined to the inside of a flexible or rigid envelope underequipressure and whose main function is to maintain a substantiallyconstant geometry over time.

All of these devices carrying a hot fluid within an insulated pipeexhibit, to different degrees, the phenomenon of differential dilation.In fact, the inside pipe, generally made of steel, is at a temperaturethat should be maintained as high as possible; for example 60 or 80° C.,since the outer envelope, which is quite frequently also made of steel,is at the temperature of the seawater; that is, around 4° C. The forcesacting on the connection elements between the inside pipe and the outerenvelope are considerable and can reach several tens, even severalhundreds of tons and the overall resulting elongation is of the order of1 to 2 m in the case of insulated pipelines of 1,000 to 1,200 m inlength.

OBJECTS AND SUMMARY OF THE INVENTION

The object proposed according to the present invention is to be able torealize and install such bottom—surface links for sub-marine pipelinesat great depths, such as greater than 1,000 meters, for example, and ofa type comprising a vertical tower and in which the transported fluidmust be maintained above a minimal temperature until its arrival at thesurface, by reducing to a minimum the components subject to heat loss,by preventing the drawbacks created by thermal expansion itself ordifferent of the various components of said tower in such a fashion asto resist extreme stresses and the fatigue phenomena accumulated overthe life span of the work, which currently exceeds 20 years.

Another object of the present invention is to provide a bottom—surfacelink installation of the hybrid tower type, whose anchoring system ishigh strength and inexpensive and wherein the installation process ofthe various constituent elements is simplified and likewise inexpensive.

Another object based on the present invention is to provide aninstallation that makes it possible to service the interior of thesub-marine pipeline resting on the sea floor using a process of thecoil-tubing type from the surface and utilizing the top end of thevertical riser.

A solution to the proposed objects is thus an installation ofbottom—surface link for sub-marine pipelines resting on the seafloor, inparticular at great depth, comprising:

a) at least one vertical riser connected at its bottom extremity to atleast one sub-marine pipeline resting on the sea bottom and having atits top extremity at least one float, and

b) at least one connecting pipe, preferably a flexible pipe, assuringthe connection between a floating support and the upper extremity ofsaid vertical riser, and

c) the connection between the lower extremity of said vertical riser anda so-called sub-marine pipe resting on the sea bottom is provided bymeans of an anchoring system comprising a foot positioned on the bottomand remaining in place especially by its own weight or by means ofsuction anchors;

characterized in that:

1. said vertical riser comprises at its lower extremity a portion ofterminal pipe, preferably reinforced, connected to the upper part ofsaid vertical riser by a flexible joint which allows angular movements(α) of said upper part relative to said portion of the terminal pipe;

2. the terminal part of said pipeline resting on the sea bottom has anterminal curvature in the shape of an elbow, preferably with a largeradius of curvature;

3. the lower extremity of said terminal portion of the vertical riser isconnected to the upper extremity of said elbow shaped terminal curvatureof the sub-marine pipeline resting on the sea bottom by a singleconnecting element between said vertical riser and said sub-marinepipeline resting on the bottom, preferably an automatic connector, and

4. said foot rigidly maintains in fixed vertical position and connectedone to another by means of said connecting element:

-   -   on the one hand, said terminal elbow shaped pipe of said        vertical riser    -   on the other hand, said terminal elbow shaped curvature of said        sub-marine pipeline resting on the bottom, the latter being        turned facing upwards.

The installation according to the present invention is advantageous,because it has a static geometry of the lower part of the tower and itis thus completely stabilized and does not bear any movement and/orforce, especially at connection between the vertical riser and the piperesting on the sea bottom.

A further advantage of the present invention- is also the considerablereduction of the overall cost resulting from the suppression of theconnection sleeves used in the prior art for connecting the verticalriser and the pipe resting at sea level. In fact, such a connectionsleeve, according the prior art, is complex to manufacture and install,because it is installed after lowering to the bottom of the extremity ofthe pipe resting on the sea bottom and after installation of the foot,which is done in a target zone each generally representing,respectively, a circle of approximately 5 to 10 meters in diameter; thatis, with a considerable uncertainty as to their relative position.Metrology of the position and relative orientation of the extremities ofthe lines should be done then using a ROV (“remote operated vehicle,”meaning an automatic sub-marine remote controlled from the surface). Theconnection sleeve is then realized either on the mainland or on boardthe installation vessel, then put into place using a ROV. In addition,such a connection sleeve requires connecting means, generally twoautomatic connectors, one at each end of the connection sleeve, betweenthe vertical riser and the pipe resting on the sea bottom. Finally, itmust be stated that the effective thermal insulation of such a bentconnection sleeve equipped with its automatic connectors used in theprior art is extremely complicated to produce and is therefore veryexpensive, which accordingly considerably increases the cost and thecomplexity of the installation in the case, wherein it is implementedunder conditions requiring extreme insulation.

Finally, because the extremities of the pipe resting on the bottom arelowered into the target zones and distanced from the base of the tower,it is necessary to install prefabricated connection sleeves having asuccession of linear and variable angular bent parts for connecting theextremity of the pipe resting on the bottom to the base of the tower,which creates considerable forces—by the pressure and the movementcreated by the dilation of the pipe resting on the bottom—in saidconnection sleeves, giving rise principally to flexion stresses due tothe existence of said bends themselves.

The installation according to the invention makes it possible toeliminate all of these drawbacks of the prior art and to more costeffectively provide a riser tower incorporating the best performanceinsulation technologies.

According to WO 00/49267, the tower comprising several risers issuspended by a central tendon that holds a plurality of vertical risersin suspension and the top of the tendon held by a float constitutes apoint of reference substantially fixed at altitude at the variationclose to the overall apparent weight of the risers and their contents;and the integrality of displacement was thus accommodated by the bendconnection sleeves on the lower part, expensive parts and difficult toproduce and install. According to the present invention, thesubstantially elevated fixed point is situated below the tower at thelevel of the flexible joint, which makes it possible to eliminate thebent connection sleeves, the differential movements between the risersbeing accommodated by the different floats that are free to displacevertically at the top of each of said risers.

In one advantageous embodiment, said foot comprises:

a) a lower structure positioned on the bottom that maintains saidterminal elbow of said pipe in vertical position turned upwards and afirst part of said connection element at the extremity of said bend, and

b) an upper structure that assures guidance of said terminal part ofsaid vertical riser and that holds it in the vertical position and thatcooperates with said lower structure such that said upper structure ispositioned over said lower structure, so as to:

-   -   guide a second part of said connection element situated at the        lower extremity of said terminal part of said vertical riser        relative to said first complementary part of said second part of        said connection element, and    -   stabilize said lower structure positioned on the bottom by the        weight of said upper structure and, eventually, in cooperation        with suction anchors.

This embodiment described above makes it possible in effect tofacilitate connection of the vertical riser and the sub-marine piperesting on the bottom when the installation is put into place.

Preferably, said lower structure is secured to said upper structure by asystem of wedges, which prevents any subsidence of said lower structureinto the sea floor.

More particularly, said upper structure comprises:

-   -   a main structure and stabilization elements that cooperate with        said main structure for stabilizing it on the sea bottom;    -   a central elevated structure comprising:    -   an interior cavity open at its base and having a form        complementary to the external form of said lower structure such        that said central structure caps said lower structure, and    -   an upper opening crossed by said terminal portion of said        vertical riser, which latter being blocked in said opening by a        second wedge system, said opening communicating with said        interior cavity, and    -   a lower peripheral horizontal platform at the base of said        central structure with which said stabilization elements        cooperate, in particular on which the anchor block or across        which the suction anchors are imbedded in the floor.

The present invention is particularly advantageous if the installationcomprises:

-   -   at least two said vertical risers substantially parallel and in        proximity, each being connected at its upper extremity to at        least one float, and    -   said foot holding [them] in vertical fixed position and        connected to each other by means of said connection elements:    -   on the one hand, two said portions of the terminal pipes of said        vertical risers and    -   on the other hand, respectively, two so-called terminal elbow        bends of two so-called sub-marine pipelines resting on the        bottom, these latter being turned upwards.

In this embodiment with a plurality of risers, said foot comprises:

-   -   at least two so-called lower structures positioned on the        bottom, each holding in vertical position turned upwards one        so-called terminal bend of one so-called sub-marine pipe resting        on the sea bottom and one so-called first part of a so-called        connection element at the extremity of said bend, and    -   one so-called upper structure that assures guidance of the two        so-called terminal portions of said vertical risers and holding        them in vertical position and which,-cooperates with the two        so-called lower structures such that said upper structure is        positioned above at least two so-called lower structures        side-by-side in such a fashion as to guide one so-called second        part of said connection element situated at the lower extremity        of said terminal portion of each of said vertical risers        relative to said first part of said connection element at the        extremity of said bend of each of said conduits resting on the        bottom by the weight of said upper structure and eventually by        cooperating with the suction anchors.

In one particular embodiment, said upper structure comprises a mainstructure comprising at least two interior cavities, each one of a formcomplementary to the external form of on so-called lower structure andcapping it and at least two so-called upper openings, each communicatingwith one so-called interior cavity, each of said upper openings beingcrossed by one so-called terminal portion of said vertical risers, theselater being blocked in said upper opening by a so-called second systemof wedges.

Advantageously, said main structure comprises:

-   -   at least two elevated central structures cooperating with a        second horizontal platform on which at least the two so-called        lower structures rest;    -   said second platform being surmounted by a central vertical        element that makes possible:    -   guiding of said vertical risers relative to said upper openings        of each of said elevated central structures, and    -   preferably also the blocking of the two so-called elevated        structures using a wedge system.

The installation according to the invention is more particularly stilladvantageous if:

-   -   the two so-called sub-marine pipelines resting on the sea floor        are assembled in a bundle in the same flexible protective        envelope making it possible to contain an insulating material,        preferably a phase change of the paraffin type or a gel        insulating compound, surrounding said pipes and    -   said vertical riser comprises in its upper part above said        flexible joint a system of insulated pipes comprised of an        assembly of two coaxial pipes comprising an internal pipe and an        external pipe, an insulating fluid or material, preferably a        phase change material of the paraffin type or a gel compound        being placed preferably between the two so-called pipes or even        by maintaining a forced vacuum between these latter.

In one preferred embodiment for facilitating the differential movementsbetween risers, a first and a second vertical riser are maintainedsubstantially parallel by means of a sliding connecting system allowingaxial displacements of said first riser relative to said second riser,said connecting system comprising a tubular collar fixed around saidfirst riser, said collar being rigidly connected to a tubular ringsliding freely around said second riser, preferably a plurality ofso-called collars of the same sliding connecting system being disposedalong each of said risers alternatingly with said rings of anotherso-called connecting system on the same so-called riser. This slidingconnecting system makes it possible for the risers to move verticallybut not transversely; that is, they remain substantially equally spacedin a plane perpendicular to their axes.

The junctions between the different components of the float assembly,flexible pipeline and vertical riser being situated not far from thesurface are subjected to the combined effects of swell and current. Inaddition, the surface support being subjected not only to swell andcurrent but also to the effects of wind, the movements of the assemblycreate at the singular point that constitutes the junction between theriser and flexible pipeline, considerable forces in the variousmechanical constituents. In fact, the float exerts a vertical tractionupwards that can vary by several tens of tons to several hundreds oftons even exceeding 1,000 tons, depending on the depth of the water thatcan reach 1,500 m or even 3,000 m and according to the inside diameterof the pipe that can vary from 6″ to 14″ or even 16″. Thus, the forcesto be transmitted are considerable and the movements of the assembly arecadenced, inter alia, to the rhythm of the swell; in other words, with atypical variant period, in rough period between 8 and 20 seconds. Theaccumulated fatigue cycles over the life span of the field thus reachingvalues exceeding several tens of millions of cycles. That is why aninstallation according to the invention advantageously comprises atleast one float, preferably a group comprising a plurality of floatsinstalled at the top of each, at least two so-called vertical risers,disposed in such a fashion that said floats are held secured by means ofa structure supporting them and allowing vertical displacements relativeto each of said float groups relative to each other, in particulardisplacement caused by differential dilation. Said floats are thus freeto move vertically but thy are sufficiently spaced so that, at the mercyof deformation of their carrying structures, any physical contactbetween groups of floats is prevented.

Another object of the present invention is to make possible facilitatedintervention to the interior of said riser from the surface, inparticular to enable inspection or cleaning of said vertical riser, bythe introduction of a rigid tube from the upper extremity of the float,passing through said connecting device between the float and thevertical riser.

In fact, these bottom—surface connections transport a polyphasic fluid;in other words, a fluid comprised of crude petroleum, water and gas.When the fluid rises, the local pressure falls and the gas bubbles thusincrease in volume, creating phenomena of instability of the fluid veinthat can result in significant surges. At production stoppages, the gasis situated in the upper part and the oil-water mixture is trapped inthe lower parts; that is, in the lower part of the catenary flexiblepipe zone, as well as in the lower part of the substantially verticalsection of the riser.

The polyphasic mixture, made up of crude petroleum, water and gas has atendency, when the temperature falls below a level situated between 30and 40° C., to create two types of plug that risk blocking production. Afirst type of plug is due to the formation of hydrates from the gasphase in the presence of water; another type is due to setting of theparaffin contained in variable proportion in the crude petroleum ofcertain oil fields, particularly in West Africa.

The so-called “coiled tubing” service method is known for the interiorof the pipelines that consists of urging a rigid tube having a smalldiameter, generally 20 to 50 mm, through the pipe. Said rigid tube isstored wound up by simple wrapping around a reel, then untwisted at thetime of unwinding. Said tube can measure several thousands of meters inone single length. The end of the tube situated on the drum storage reelis connected by a rotating joint to a pumping device that is capable ofinjecting a liquid under high pressure and temperature. Thus, by urgingthe end of the tube through the pipeline, while maintaining pumping andcounter-pressure, the concerned pipeline is cleaned in virtue of theinjection of a hot product capable of dissolving the plugs. This servicemethod is currently used in servicing vertical wells or in pipesobstructed by the formations of paraffins or hydrates, phenomena thatare current and dreaded in all crude petroleum production installations.The coiled tubing method is called ‘continuous tubing cleaning’ or NTCin the following.

The installation according to the invention comprises a linking devicebetween said float and the upper extremity of said riser, comprising:

-   -   a second flexible pipe whose extremities are incorporated at the        respective level of said float and the upper extremity of the        riser;    -   linking of said second a second flexible pipe at the upper        extremity of said riser to the upper extremity of said riser        being formed by means of a gooseneck device, which gooseneck        device assures also the connection between said riser and a        so-called linking pipe with the floating support, preferably a        so-called flexible pipe;    -   said second flexible conduit being preferably extended through        said float by a rigid tubular channel passing through the float        from one side to the other in such a fashion that service can be        done at the interior of said vertical riser from the upper part        of the float through said rigid tubular channel, then said        lining device comprised of said second flexible pipe is through        said gooseneck device in such a fashion as to access the        interior of said riser and clean it by injection of liquid        and/or scraping of the inside wall of said riser of said        sub-marine pipeline resting on the sea floor.

The gooseneck device comprises an upper straight linear part thatassures the junction between said vertical riser and said secondflexible pipe connected to said float. A curved part in the shape of anelbow disposed on this so-called straight linear part of the gooseneckdevice makes possible the junction between the extremity of saidvertical riser and the extremity of said flexible pipe itself connectedto said floating support. The extremities of said curved part beingsubstantially tangent to the curve of the catenary comprised of saidflexible pipe that assures the linking to the floating support andsubstantially tangent to said straight linear part of the gooseneckdevice.

A further advantage of the installation according to the invention isthat all of the elements can be prefabricated on the mainland prior tobeing installed. They can thus be assembled in mock in order to verifythat all of the elements cooperate correctly, including the screw means;thus, assembly of the installation is considerably simplified and theoperational time of the installation vessels is reduced to a minimum. Inthe prior art, the sub-marine pipelines were positioned and then, afterinstallation of the risers, the elbow connection sleeves were fabricatedon the basis of high-precision metrology using ROVs. The connectionsleeve, prefabricated on the mainland or on site can measure severaltens of meters and must them be installed using the same ROV, whichrepresents a considerable operational time and consequently very highcosts due to the sophistication of the specialized installation vessels.The gain realized by the device and the process according to theinvention, works out to several days of installation vessel as well asto the elimination of the indispensable automatic connectors at each endof the prefabricated connection sleeve, which represents a considerablereduction in costs.

The objects of the present invention are thus similarly achieved by amethod for implementing an installation that comprises the steps,wherein:

-   -   at least one so-called sub-marine pipeline, whose terminal part        has a so-called elbow turned facing upward and stabilizing it on        the sea floor, is installed on the sea floor and    -   a so-called foot is lowered that maintains said elbow bend in        place and stabilizes it on the sea floor, and    -   at least one so-called vertical riser is lowered through an        opening in said foot, the lower extremity of said riser        comprising a so-called second complementary part of a so-called        connection element, in particular male or female, respectively,        in such a fashion as to realize said connection between the two        so-called first and second complementary parts of said        connection element, and    -   the blockage in said foot of said lower terminal part of said        riser (5 ₁) and said terminal part of pipeline resting on the        sea floor having a so-called elbow-type bend.

More particularly, the method according to the invention-comprises thesteps, wherein:

1- at least on so-called sub-marine pipeline is installed on the seabottom, the terminal part of which has an elbow-type bend secured to aso-called lower structure, preferably previously installed at thesurface, and

2- a so-called upper structure is lowered over said lower structure andsaid lower structure is blocked mechanically, preferably still by meansof a system of wedges, at the interior of said cavity of said upperstructure, and

3- said upper structure is stabilized by the cooperation of saidstabilization elements with the bottom from above a so-called baseplatform of said upper structure resting on the bottom, in particular bylowering of the anchorage base onto said platform or by imbedding thesuction anchors through an opening in said platform;

4- at least one so-called vertical riser is lowered through at least oneso-called upper opening of said upper structure, then

5- after approximation of the complementary parts of said connectionelement, said connection is made, and

6- blockage of said portion of the terminal pipe at the lower extremityof said vertical riser is done between said connection element and saidflexible joint in said upper opening using a system of wedges.

In a preferred embodiment, the blockage of said lower structure using asystem of wedges detailed above at step 2 is done at the end; that is,after the final step 6.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the light of the detailed explanation of the embodimentsthat follows with reference to the attached FIGS. 1 to 12.

FIG. 1 represents a view in section of the upper part of a hybrid towerconnected to a FPSO type floating support with a vessel 10 performing aservice operation on the vertical of said tower.

FIG. 2 represents a view of the lower part of the installation accordingto the invention prior to connection of the lower extremity of thevertical riser with said sub-marine pipeline resting on the sea floor.

FIG. 3A represents a side view of the lower part of the installationaccording to the present invention after connection of the verticalriser and prior to blockage in the foot.

FIG. 3B represents a view from above of the system of wedges used incentering blocking of the vertical riser in the foot.

FIG. 4 is a view in section of the lower part of the installationaccording to the invention, after blocking—centering of the riser in thefoot and showing possible angular movements of the upper part of thevertical riser as well as an anchorage block and a suction anchor.

FIGS. 5A and 5B are views in section respectively of the side (FIG. 5A)and the face (5B) of a lower structure having a pedestal type pyramidalstructure. In FIG. 5A, the cross-section corresponds to a section alongthe axis AA of FIG. 5B.

FIG. 6 is a side sectional view of the lower part of the installationaccording to the invention, comprising two vertical risers installed inparallel and connected at their bas to two sub-marine pipelines restingon the sea floor, assembled in a bundle.

FIG. 7 is a cross-section view representing the sections of an internalpipe and an external pipe of a vertical riser insulated by pipe-in-pipeassembly.

FIG. 8 represents a cross-section view of a section of a bundle ofsub-marine two pipes resting on the sea floor.

FIG. 9 is a side view of two vertical risers secured by connection meansand sliding guide means.

FIG. 10 represents a side view of the upper extremity of the verticalrisers with a gooseneck type device enabling their connection on the onehand to the floating support by means of a flexible pipe and on theother hand to the floats.

FIGS. 11 and 12 represent, respectively, side and top views of floatssituated in direct continuity with the vertical risers.

FIGS. 13 and 14 represent an embodiment with a second platformsurmounted by a central vertical guiding element.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 represents a bottom-to-surface connection for an sub-marinepipeline 10 resting on the sea bottom, in particular at great depth,comprising:

a) at least one vertical riser 5 connected at its lower extremity to atleast one sub-marine pipeline 10 resting on the sea bottom (not shown)and at its upper extremity to at least one float 6, and

b) at least one connection pipeline, preferably a flexible pipeline,assuring the connection between a floating support 1 and an upperextremity 4 of said vertical riser.

The FPSO 1 is anchored over an oil field at 1,500 m depth by ananchoring system (not shown) and comprises at its side a supportingsystem 2 of flexible pipelines 3 for petroleum effluents 3 configured asa catenary rising towards a gooseneck device 4, itself secured at itsupper extremity to a vertical riser 5. The assembly is maintained undertension by said float 6 installed at the head of the vertical riser 5 bymeans of a flexible pipe 7 for opening onto a closed opening by a valve9. A service vessel 10 situated vertical to said float can carry out amaintenance operation by coil tubing through the float 6 in such afashion as to force into the vertical part of the pipeline a smalldiameter rigid pipe (not shown)—generally 50 mm—for cleaning theinterior of the pipeline along its progression. The coil tubing devicesbeing known to the specialist in the field of petroleum well service arenot developed in greater detail herein.

FIGS. 3A and 4 represent the connection between the lower extremity ofsaid vertical riser and a so-called sub-marine pipeline 10 resting onthe sea bottom by means of an anchoring system comprising a foot 13-14positioned on the bottom and remaining in place in virtue of its ownweight.

Said vertical riser comprises at its lower extremity a terminal pipeportion 5 ₁, preferably reinforced, connected to the upper part 5 ₂ ofsaid vertical riser by a flexible joint 19, which allows angularmovements α of said upper part 5 ₂ relative to said terminal pipeportion 5 ₁.

The flexible joint 19 allows a significant variation in the angle abetween the axis of the tower and the axis of the part of the verticalriser secured to the foot without giving rise to significant stresses inthe portions of the pipeline situated on either side of said flexiblejoint. This flexible joint can be, in known fashion, either a sphericalball with leakproof joints or a laminated ball comprised of sandwichesof elastomer sheets and adhered metal sheets capable of accommodatingthe significant angular displacements by deformation of the elastomers,whilst conserving complete leak tightness due to the absence of frictionjoints, or even a limited length of flexible pipeline capable ofproviding the same service. In all cases, it is understood that theso-called flexible joint 19 is hollow and its inside diameter issubstantially of the same diameter as the adjacent pipes comprising saidvertical riser 5 in such a fashion as not to interfere with and tofacilitate the passage of scraping tools or coil tubing servicing.

Said terminal part 11 of the pipeline resting on the sea floor has anelbow-type bend, preferably with a large radius of curvature, inparticular a radius of curvature of greater than 5 meters and moreparticularly of the order of 5 to 10 meters. According to the presentinvention, an “elbow” is defined as two short rectilinear sections ofpipe disposed at 90° to each other, separated and connected between eachother by a curved section having said radius of curvature.

The lower extremity of said terminal portion 5 ₁ of the vertical riseris connected to the upper extremity of said terminal curvature 11 of thesub-marine pipeline resting on the bottom by a single connection element12 between said vertical riser and said sub-marine pipeline resting onthe bottom 10, preferably an automatic connector.

Said foot 13-14 rigidly maintains in the vertical position and connectedto each other by means of said connection element 12:

-   -   on the one hand said portion of the terminal pipe 5 ₁ of said        vertical riser and    -   on the other hand said elbow-type terminal bend 11 of said        sub-marine pipeline resting on the bottom, which latter is        turned facing upwards.

According to FIG. 2, said foot comprises:

a) a lower structure 12 positioned on the bottom that maintains saidelbow-type terminal bend 11 of said pipeline resting on the bottom 10and a first part 12 ₁ of a so-called connection element 12 in verticalposition, turned upwards at the extremity of said curvature and

b) an upper structure 14-18 that assures guidance of said terminalportion 5 ₁ of said vertical riser that it maintains in verticalposition and that cooperates with said lower structure 13 in such afashion that said upper structure 14-18 is positioned above said lowerstructure 13 in such a fashion as to guide a second part 12 ₂ of saidconnection element 12 situated at the lower extremity of said terminalportion 5 ₁ of said vertical riser opposite to said first complementarypart 12 ₁ of said second part 12 ₂ of said connection element 12 and insuch a fashion as to stabilize said lower structure 13 positioned on thebottom in virtue of the weight of said upper part 14-18. The lowerstructure 13 is a light pedestal-type metal structure which isintegrated at the elbow-type extremity of said pipeline resting on thebottom of the sea 10. FIG. 2 represents one of two complementary partsof the connection element 12; that is, a male part 12 ₁ capable ofconnecting to a female part 12 ₂ of the lower extremity of said terminalportion 5 ₁ of the vertical riser 5 (FIG. 4).

The principle of the automatic connectors 12 being known to thespecialist in the art in the field of hydraulics and pneumatics will notbe described in detail herein. This mode of connection has the advantageof being entirely reversible, insofar as the automatic connector isdesigned to be able to be disconnected. It is thus possible, in thecourse of exploitation, to perform service on a single riser fordismantling it and replacing it without disturbing the rest ofproduction and thus without having to shut down production of adjacentrisers.

In FIG. 2, said upper structure 14-18 comprises more specifically:

-   -   a main structure 14 and stabilizing anchoring blocks 17, that        are positioned on the main structure 14,    -   said main structure 14 in the form of a hat, comprises:    -   a central structure 14 ₁ in elevation geometrically externally        cylindrical in square or cylindrical cross-section and closing        off an interior cavity 21 open at the base of said central        structure, said cavity 21 having a flared shape enlarging        towards the base and complementary to the pyramidal external        shape of said lower structure 13 in such fashion as to cap said        latter. Said central structure 14 ₁ comprises an upper opening        (20) traversed by said terminal portion 5 ₁ of said vertical        riser 5, the latter being blocked in said opening 20        communicating with said interior cavity 21 and    -   a lower peripheral horizontal platform 14 ₂ at the base of said        central structure 14 and surrounding same, on which said anchor        blocks 17 ₁ are placed.

Said lower structure 13 is a hollow pyramidal pedestal-type structuretruncated at its top and laterally transversed at its base by theterminal part bend 11 of the pipeline resting on the bottom 10, whichopens at its top onto the flat part 13 ₁ on which the male part 12 ₁ ofthe connection element 12 at the extremity of the pipeline 10 rests.

In FIG. 4, the base 14 ₂ comprises in the rightmost part of the drawing,vanes 14 ₃ taking up the pressure forces due to the dilation of thepipeline 10 as well as an anchor block type stabilization element 17 ₁.

In fact, the pipeline resting on the bottom of the sea is substantiallyin alignment up to the foot of the tower; that is, up to the footstructure. Variations in temperature bring about forces internal to thepipeline that create a horizontal pressure on the foot parallel to theaxis of said pipeline that can reach several tens of tons. These vanes14 ₃ are disposed preferably perpendicular to the axis of the pipelineand penetrate deeply into the floor in such a fashion as to containthese pressure forces and prevent any displacement of said foot. For thesake of clarity in the description of the base in the various otherfigures, said vanes 14 ₃ have not been shown.

In the case of a foot stabilized by a suction anchor 17 ₂ the designitself of the suction anchor 17 ₂ is well adapted to absorbing suchforces. In the leftmost part of FIG. 4 a suction anchor 17 ₂ isrepresented imbedded through an opening 37 ₀ in the platform 14 ₂. Thesuction anchors 17 ₂ have channels in the form of a large diameter belland generally elongated, having on the lower face an open opening and onthe upper face a leakproof plug 37 ₁. The anchor 17 ₂ is lowered bymeans of a crane lug 37 ₂ until penetrating the floor. A ROV (not shown)then connects on the opening 37 ₃ and, with the aid of a pump, appliessuction to the interior of the bell. The resulting force tends to causethe suction anchor to penetrate into the sea floor until the shoulder 37₄ abuts on the platform 14 ₂ of the foot structure and-so stabilizes.This type of anchor 17 ₂ can measure several meters in diameter and 10to 30 m in height, or more. They can weigh from 15 to 50 tons each, ormore.

In FIGS. 3A, 4 and 5A said lower structure 13 is secured by said upperstructure 14-18 by a system of wedges 15.

FIGS. 5A and 5B are cross-sectional views, respectively, of the side andface of the pedestal-type structure 13. In FIG. 5A the cross-sectioncorresponds to a slice along the axis AA and details the faces 100 ofsaid pedestal 13 cooperating with the hereinbefore described wedges 15.Said wedges 15 (not shown in FIG. 5B) have a length corresponding to thewidth of an opening 101 in the pedestal structure 13. The pedestal 13 isrepresented with an identical counterpart in the main structure 14 insuch a fashion that the pedestal assembly 13 plus the structure 14 formonly one, once the wedges 15 are locked.

In FIG. 6 an installation is represented, which comprises:

-   -   at least two so-called vertical risers 5 a, 5 b substantially        parallel and in proximity, each being connected at its upper        extremity to at least one float 30 a, 30 b and    -   said foot 14-18 maintaining them in fixed vertical position and        connecting them to each other by means of said connection        elements 12:    -   on the one hand two so-called terminal portions of the pipeline        5 ₁ of said vertical risers and    -   on the other hand, respectively, two so-called elbow-type        terminal bends 11 of two so-called sub-marine pipelines resting        on the bottom 10, these being turned facing upwards.    -   two so-called lower structures 13 a, 13 b positioned on the        bottom, each holding in vertical position, turned upwards one        so-called terminal bend 12 of a so-called sub-marine pipeline 10        ₁, 10 ₂ resting on the sea bottom and a first part 12 ₁ of a        so-called connection element 12 at the extremity of said bend 11        and    -   a co-called upper structure 14-21 that assures guidance of the        two so-called terminal portions 5 ₁ of said vertical risers 5 a,        5 b and maintaining them in vertical position and that cooperate        with the two so-called lower structures 13 a, 13 b in such a        fashion that said upper structure 14-21 is positioned over and        caps two so-called lower structures 13 a, 13 b side-by-side in        such a fashion as to guide a so-called second part 12 ₂ of said        connection element 12 situated at the lower extremity of said        terminal portion 5 ₁ of each of said vertical risers opposite to        said first part 12 ₁ of said connection element 12 at the        extremity of said bend of each of said pipelines 10 ₁, 10 ₂        resting on the sea bottom and stabilizing said lower structures        12 positioned on the sea bottom in virtue of the weight of said        upper structure 14-21.

Said upper structure comprises a main structure 14 comprising two lowercavities 21 opened at the base and each having towards the bottom aflanged shape complementary to the external pyramidal shape of oneso-called lower structure 13 a, 13 b and capable of capping it and twoso-called upper openings 20 each communicating with a so-called lowercavity 21, each of said upper openings 20 being traversed by saidterminal portions 5 ₁ of said vertical risers 5 a, 5 b, these latterbeing centered and blocked in said upper openings 20 by said secondsystem of wedges 18.

In FIGS. 6 and 7, said vertical riser 5 comprises in its upper part oversaid flexible joint 19 a system of pipes comprised of a pipe-in-pipetype thermal insulating system comprising an assembly of two coaxialpipelines comprising an internal pipeline 5 ₂ and an external pipeline 5₃, an insulating fluid or insulating material 5 ₄ comprised, forexample, of paraffin, being placed preferably between the two so-calledconduits 5 ₂, 5 ₃.

In FIGS. 6 and 8, the two so-called sub-marine conduits 10 ₁, 10 ₂resting on the sea bottom are assembled in a bundle in the sameencircling flexible protective envelope 10 ₃ making it possible tocontain an insulating material 10 ₂, preferably comprised of paraffin,surrounding said conduits.

In FIG. 4, all of the constituent elements of the base of the tower arein final configuration, the overall geometry of the assembly no longerable to move, except in the vertical part of the riser situated abovethe flexible joint 19.

FIG. 6 represents the lower part of a tower similar to that of FIG. 5,comprising tow vertical risers 5 a, 5 b connected to two independentpipelines 10 ₁, 10 ₂. The risers are installed in parallel according tothe procedure hereinbefore described.

FIG. 9 details a preferred manner for permitting the axial displacementsof one of the risers 5 a, 5 b relative to the other in such a fashionthat the differential dilation between risers can be released and notinduce unacceptable stresses that risk damaging or even destroying thetower. The device according to the invention is comprised of a tubularcollar 25 firmly fixed on the riser 5 a and rigidly connected on 27 to atubular ring 26 freely sliding on the riser 5 b. The collars aredisposed along the length of the risers, whether or not in regularintervals, and preferably installed in opposition as represented in thesame figure. Thus, the two risers being secured to the foot at the levelof the flexible joints 19, if only the riser 5 a is at temperature thesliding rings 26 allow expansion of said riser 5 a and thequasi-integrality of the expansion is at the head of the vertical riser,at the level of the gooseneck as indicated in FIG. 10.

In FIG. 10, the installation comprises a linking device 4, 7 betweensaid float 6 and the upper end of said riser 5, comprising:

-   -   a second flexible pipeline 7 the extremity of which are embedded        respectively at the underside of said float 6 and the upper end        of riser 5    -   a second flexible pipeline 7 at the upper extremity of said        riser 5 formed by means of a gooseneck device 4, said gooseneck        device 4 assures also the connection between said riser 5 and a        so-called flexible conduit 3 with the floating support;    -   said second flexible pipeline 7 being extended through said        float 6 by a rigid tubular conduit 8 crossing the float from one        side to the other so that access is possible to the interior of        said vertical riser 5 from the upper part of the float 6 through        said rigid tubular conduit 8, then said connection device        comprised of said second flexible pipeline is through said        gooseneck device 4, so as to access the interior of said riser 5        and clean it by injection of liquid and/or by scraping the        inside wall of said riser (5), then that of said sub-marine        pipeline 10 resting on the sea bottom.

Said second flexible pipeline 7 has at its extremities progressiveinertial variation elements in section 7 ₁, 7 ₂ at the level,respectively, of the underface of the float 6 and the upper extremity 41of the gooseneck.

In FIG. 11, the installation according to the invention comprises twogroups each comprising a plurality of floats 30 a, 30 b at the top ofthe at least two so-called vertical risers 5 _(a), 5 b. Said floats 30a, 30 b of a same so-called group are maintained secured and fixedrelative to each other by means of a rigid structure in the form of arectangular frame comprised of two parallel vertical bars 33 and twoparallel transverse bars 36 securing and supporting them. The tworectangular frames of the two groups of floats 30 a, 30 b are connectedto each other by two articulated frames in the form of a parallelogramon each side, each comprised of two parallel, substantially verticalbars 33 and connected at their extremities by articulations 35 to theextremities of the upper 34 a and lower 34 b parallel transverse bars.

The assembly formed in deformable parallelepiped by vertical translationof said rectangular frames relative to each other, authorizes relativevertical displacements of each of said float groups relative to theother, brought about in particular by differential dilation.

As shown in detail in FIGS. 11 and 12, the structure supports a group ofthree floats 30 a, whose central float is traversed by a pipeline 8 incontinuation of the flexible pipe 7 and opening at the upper part ofsaid float over a leakproof opening 9; for example, a spherical gatevalve. Thus, all of the maintenance operations on the riser and on alarge part of the pipeline resting on the sea bottom are doneadvantageously from a surface vessel 10 installed on the vertical planeof said access valve 32 a; the coil tubing operation being possible inthe part of the tube resting on the sea bottom, on condition that theradius of curvature of the bend situated in the boot is sufficientlylarge, for example 5 m, or even 7 m or more.

In FIG. 10, the riser 5 b, being cold, is shorter than the riser 5 a,which is at a higher temperature. Likewise, in FIG. 11, the float group30 b is offset downwards substantially by the same distance. The twofloat groups 30 a, 30 b are maintained substantially at the samedistance by means of the structures in parallelogram forming deformableparallelepipeds vertically, authorize the vertical displacements broughtabout, for example, by the differential dilation of the two risers 5 a,5 b, the one being hot 30 a and the other being at the temperature ofthe sea water; that is, cold.

The connection means of the floats have been described by means of bars33, 34 articulated at the level of the axes 35, but being quite capablealso of being realized by deformable elements, for example elements madeof elastomers, it being understood that the result sought is to maintainat a substantially constant distance the two float groups 30 a-30 b inorder to prevent them from clashing against each other as the result ofswell and current, whilst allowing relative movements in a directioncorresponding substantially to the axis of the vertical pipelines.

In the same way, in FIG. 9, it is within the scope of the invention ifthe sliding collars 25 and rings 26 are used to guide the two verticalrisers in the running part by articulated bars similar to thosehereinbefore described for guiding the floats 30.

The vertical riser 5 can be either prefabricated on the mainland andthen towed to the site or fabricated directly on the site shortly beforeinstallation. It is comprised of a running riser portion 5 at the lowerextremity of which a flexible joint 19 is installed connected to aportion of reinforced riser 5 ₁, itself secured to the second part 12 ₂of the automatic connector. The internal passage of the flexible joint19 as well as the portion of the reinforced riser 5 ₁ have an insidediameter that is preferably identical to that of the riser 5. Saidportion of the riser 5 ₁ is reinforced in order to assure rigidity ofthe assembly once the wedges 18 are locked into their final position.Said reinforcement results either from a simple increase in thethickness of the wall or by the addition of external stiffeners or fromthe combination of the two or by any other means intended to provide theassembly with increased strength and rigidity.

In the method for implementation of the installation according to theinvention, the steps are carried out, wherein:

1- at least one so-called sub-marine pipeline 10 is installed on the seabottom, whose terminal portion has a elbow-type bend 11 and is securedto said lower structure 13, which is preferably previously installed onthe surface and at the extremity of which a male 12 ₁ or a female 12 ₂part of a so-called connection element 12 is affixed and

2- a so-called main structure 14 is lowered over said lower structure 13and preferably is blocked mechanically, more preferably still using asystem of wedges 15 actuated, for example, by hydraulic actuators, saidlower structure 13 at the interior of said cavity 21 of said mainstructure 14 that thus form a highly rigid assembly;

3- said main structure 14 is stabilized by lowering anchorage blocks 17₁ from the surface over a so-called peripheral platform 14 ₂ resting onthe sea bottom, this placement is done under ROV control;

4- at least one so-called vertical riser 5 a, 5 b is lowered through atleast one so-called upper opening 20 of said upper structure 14, thenthe lower extremity of said portion of the riser 5 ₁ engaged in saidupper opening 20 comprising a so-called complementary part, respectivelyfemale 12 ₂ or male 12 ₁ of a so-called connection element 12, in such afashion as to realize said connection between the two complementaryparts 12 ₁, 12 ₂ of said connection element 12, then

5- after approximation of the complementary parts of said connectionelement 12, said connection is made, and

6- blockage of said portion of the terminal pipeline 5 ₁ to the lowerextremity of said vertical riser is made between said connection element12 and said flexible joint 19 in said upper opening 20 with the aid of asystem of wedges 18. In order to do this, the wedges 18, which willblock the lower part 5 ₁ of the riser situated between the connector 12and a flexible joint comprised of an articulated abutment with integralpassage 19. The wedges 18, represented in FIGS. 3 a and 3 b in retractedposition on the right and in the engaged position on the left, areactioned by a ROV by means of hydraulic actuators (not shown).

In an embodiment of the invention comprising at least two verticalrisers 5 a, 5 b, they are installed independently of each other and theyare maintained substantially parallel in the same plane over the entireheight by collars 25 and sliding rings 26 or by any other means allowingrelease of the translations in a direction parallel to the axis of saidrisers.

In FIG. 13, a second platform 13 ₁ is represented on which twopedestal-type structures 13 a, 13 b are disposed on either side of acentral vertical element 13 ₂ surmounting said second platform 131 atits center.

As represented in FIG. 14, said central vertical element 13 ₂ is used asguidance of the vertical risers 5 a,. 5 b in their descent in order thatthey arrive opposite the openings 20 a, 20 b of the two centralstructures in elevation ¹⁴ _(1a) and 14 _(1b).

In the installation sequence, the steps are carried out, wherein:

1) said second platform 13 ₁, is lowered;

2) said pedestal-type structures 13 a and 13 b are lowered over saidplatform 13, these latter being installed at the extremity of thepipelines 10 resting on the sea bottom.

3) said central structures in elevation 14 _(1a) and 14 _(1b) arelowered over said pedestal-type structures 13 a and 13 b, so as to coverthem;

4) said structures in elevation 14 _(1a) and 14 _(1b) are mechanicallyblocked using a system of wedges 13 ₃ that cooperates with the centralvertical element 13 ₂;

5) the vertical risers 5 a, 5 b are lowered along the central verticalelement 13 ₂ so as to arrive opposite the openings 20 a, 20 b in theupper part of said central structures in elevation 14 _(1a) and 14_(1b);

6) the lower extremity 5 ₁ of said vertical risers is mechanicallyblocked at the interior of said openings 20 a, 20 b using a system ofwedges 18 and second counterparts 18 ₁ placed in the lower terminalportion 5 ₁ of said vertical risers 5 ₁;

7) said pedestal-type lower structures 13 a, 13 b are mechanicallyblocked in said lower cavities 21 of said central structures inelevation 14 _(1a) and 14 _(1b) using a system of wedges 15. Saidpedestal-type lower structures 13 a and 13 b comprise the firstcounterparts 16 that make possible raising said pedestal-type lowerstructure 13 a, when the wedges 15 enter into action to block thepedestal-type lower structures 13 a and 13 b, which makes possiblelocking the first part 12 ₁ of a connection element then at the top ofsaid lower structure 13 a and the complementary part of said connectionelement 12 ₂ at the lower terminal portion 5 ₁ of the vertical riser 5a.

It is understood that the locking of the connection element 12 ₁, 12 ₂by elevation of the lower structure 13, is made possible by thecombination of the following features:

1) the shape of the wedges 15 and the first counterparts 16 of the lowerstructure 13 that induce a distance of elevation of said lower structurewhen the wedges 15 cooperate with the first counterpart, and

2) the placement of the second counterparts 18 ₁ in the terminalposition 5 ₁ of the riser and the heights of the interior cavity 21 andthe pedestal-type structure 13 that command an initial spacing of thetwo complementary parts 12 ₁, 12 ₂ of the connection element, concurwith said elevation distance.

In FIG. 14, on the right of the drawing, the position of the lowerstructure 13 b prior to locking using the system of wedges 15 isrepresented. And, at the left of the drawing, the lower structure 13 ais represented in elevation relative to said second platform 13 ₁ afterlocking using the system of wedges 15 and locking of the automaticconnector 12 ₁, 12 ₂.

In this preferred embodiment, the mechanical blockage using the systemof wedges 15 of said lower structure 13 at the interior of said cavity21 of said upper structure 14, is done after the final step.

1. A bottom-to-surface connection installation for a sub-marine pipelineresting on the sea bottom, the sub-marine pipeline having a terminalpart with an upwards-facing terminal elbow bend, the installationcomprising: a first vertical riser connected at its lower extremity tothe sub-marine pipeline and at its upper extremity to at least onefloat, said at least one float exerting an upward vertical traction onsaid first vertical riser, said upper extremity of said vertical riserand said float being capable of being subjected to displacements due toswell and current; a linking pipeline assuring a connection between afloating support and said upper extremity of said first vertical riser;and an anchoring system comprising a foot positioned on the sea bottomto connect said lower extremity of said vertical riser and thesub-marine pipeline; wherein said lower extremity of said first verticalriser includes a terminal pipe portion connected to an upper part ofsaid first vertical riser by a flexible joint which permits angularmovements of said upper part relative to said terminal pipe portion;wherein said lower extremity of said first vertical riser is connectedto an upper extremity of the terminal elbow bend of the sub-marinepipeline by a single connection element between said first verticalriser and the sub-marine pipeline; and wherein said terminal pipeportion of said first vertical riser and the terminal elbow bend of thesub-marine pipeline are connected to each other by said singleconnection element which is rigidly maintained by said foot, and whereinsaid foot rigidly maintains said terminal pipe portion of said firstvertical riser in a vertical fixed position and said terminal elbow bendof said sub-marine pipeline in a fixed position.
 2. The installationaccording to claim 1, wherein: said connection element comprises a firstpart connected at the extremity of said terminal elbow bend and a secondpart connected at the lower extremity of said terminal portion of saidfirst vertical riser, said second part being complementary to said firstpart, and wherein said foot comprises, a lower structure positioned onthe sea bottom that maintains in a vertical position turned upwards saidterminal elbow bend of said pipeline and said first part of saidconnection element, and an upper structure that assures guidance of saidterminal portion of said first vertical riser and that maintains in avertical position and that cooperates with said lower structure in sucha fashion that said upper structure is positioned over said lowerstructure so as to guide a second part of said connection element, andstabilize said lower structure positioned on the sea bottom, by virtueof the weight of said upper structure.
 3. The installation according toclaim 2, wherein said lower structure is secured to said upper structureby a first system of wedges.
 4. The installation according to claim 3,wherein said upper structure comprises: a main structure; andstabilization elements that cooperate with said main structure forstabilizing said main structure on the sea bottom; said main structurecomprising a central elevated structure capping said lower structure andcomprising an interior cavity open at its base and having a flared shapecomplementary to the external shape of said lower structure such thatsaid central structure caps said lower structure, an upper openingcrossed by said terminal portion of said vertical riser, said terminalportion being blocked in said upper opening by a second system ofwedges, said upper opening communicating with said interior cavity, anda lower peripheral horizontal platform at the base of said centralstructure and with which said stabilization elements cooperate.
 5. Theinstallation according to claim 4, wherein said stabilization elementscomprise vanes disposed under said platform that imbed vertically in thesea bottom, anchorage blocks positioned over said platform and suctionanchors positioned over said platform and passing through said platformin order to be imbedded in the sea bottom.
 6. The installation accordingto claim 1, further comprising a connection device between said floatand the upper extremity of said first vertical riser, said connectiondevice comprising: a flexible pipe, whose extremities are enclosed atthe level, respectively, of the sub-face of said float and the upperextremity of said first vertical riser; the connection of said flexiblepipe at the upper extremity of said riser being formed by means of agooseneck device, which gooseneck device also assures the connectionbetween said riser and a connection pipe with the floating support. 7.The installation according to claim 1, further comprising: a secondvertical riser substantially parallel to and approximately the same sizeas said first vertical riser each of said first and second verticalrisers being connected at its upper extremity to at least one float, andsaid foot being in a fixed vertical position and connecting said firstand second vertical risers to each other by means of said connectionelements, said foot being connected on the one hand to two said terminalpipe portions of said vertical risers, and on the other hand,respectively, to two terminal elbow bends of two sub-marine pipelines,the terminal elbow bends of the sub-marine pipelines being turnedupwards.
 8. The installation according to claim 7, wherein said footcomprises: at least two lower structures positioned on the sea bottom,each holding in vertical position, turned facing upwards a terminalelbow bend of a respective sub-marine pipeline and a first part of arespective connection element at the extremity of said terminal elbowbend, and an upper structure that assures guidance of the terminal pipeportions of said first and second vertical risers and holding them in avertical position and that cooperates with said at least two lowerstructures, in such a fashion that said upper structure is positionedover said at least two lower structures side-by-side so as to guide saidsecond part of said connection element situated at the lower extremityof said terminal portion of each of said first and second verticalrisers opposite to said first part of said connection element at theextremity of said terminal elbow bend of each of the sub-marinepipelines and stabilizing said lower structures positioned on the seabottom by virtue of the weight of said upper structure.
 9. Theinstallation according to claim 8, wherein said upper structurecomprises a main structure having at least two interior cavities eachcomplementary in shape to the outer shape of lower structure and cappingsaid lower structure, and at least two upper openings each communicatingwith a respective interior cavity, each of said upper openings beingcrossed by a respective terminal portion of one of said first and secondvertical risers, said terminal portion being blocked in said upperopening by a system of wedges.
 10. The installation according to claim9, wherein said upper structure comprises a main structure thatcomprises: at least two central structures in elevation cooperating witha horizontal platform on which at least two lower structures rest; saidhorizontal platform being surmounted by a central vertical element thatmakes possible guiding of said vertical risers relative to said upperopenings of each of said central structures in elevation.
 11. Theinstallation according to claim 1, wherein the installation is for twosub-marine pipelines that are assembled in a bundle in the same flexibleprotective envelope making possible confinement of an insulatingmaterial surrounding the sub-marine pipelines.
 12. The installationaccording to claim 1, further comprising a second vertical risersubstantially identical to said first vertical riser and wherein saidfirst and second vertical risers are held substantially parallel to themiddle of a sliding connection system allowing axial displacement ofsaid first vertical riser relative to said second vertical riser, saidconnection system comprising a tubular collar fixed around said firstvertical riser, said collar being rigidly connected to a tubular ringfreely sliding around said second vertical riser.
 13. The installationaccording to claim 12 wherein said sliding connection system comprisesrespective pluralities of tubular collars and tubular rings, saidtubular collars and tubular rings being arranged in alternation on asingle vertical riser.
 14. The installation according to claim 1,further comprising at least one float at the top of said first verticalriser, said at least one float at the top of said vertical riser beingsecured by means of a supporting structure that allows verticaldisplacements of said float.
 15. The installation according to claim 14,wherein said supporting structure comprises articulated structuresformed as parallelograms deformable by vertical translation.
 16. Theinstallation according to claim 1, wherein said first vertical risercomprises in its upper part over said flexible joint a system ofinsulated pipes comprised of an assembly of two coaxial pipes comprisingan internal pipe and an external pipe, with one of an insulating fluid,material, and a vacuum being placed between said two co-axial pipes. 17.The installation according to claim 1, wherein said linking pipeline isflexible.
 18. The installation according to claim 1, wherein saidterminal elbow bend has a radius of curvature of greater than about 5 m.19. The installation according to claim 1, wherein said connectionelement is an automatic connector.
 20. A method of placing aninstallation according to claim 1, comprising the steps of: installingat least one sub-marine pipeline on the sea bottom, the sub-marinepipeline having the terminal part with the elbow bend turned upwards andat the extremity of which said single connection element is affixed;lowering said foot that maintains said elbow bend turned upwards inposition and stabilizes it on the sea bottom; and lowering said firstvertical riser through an opening in said foot, the lower extremity ofsaid first vertical riser comprising a complementary part to saidconnection element so as to establish said connection between saidcomplementary part and said connection element wherein a blockage insaid foot of said lower terminal portion of said first vertical riser isrealized, and of said terminal part of the sub-marine pipeline.
 21. Themethod according to claim 20, wherein: at least one sub-marine pipelineis installed on the sea bottom, the elbow bend of which is secured by asingle lower structure; the method further comprising lowering an upperstructure over said lower structure until it is mechanically blocked,said lower structure being at the interior of an interior cavity of saidupper structure; stabilizing said upper structure by cooperation of saidstabilization elements using the floor above a platform at the base ofsaid upper structure resting on the sea bottom; lowering at least onesaid first vertical riser through at least one upper opening of saidupper structure then establishing said connection between saidcomplementary parts and said connection element; and blocking saidportion of the terminal pipe portion at the lower extremity of saidfirst vertical riser between said connection element and said flexiblejoint, in said upper opening using a system of wedges.
 22. The methodaccording to claim 21, further comprising the step of blocking saidlower structure at the interior of said interior cavity after saidportion of the terminal pipe portion is blocked.